Solvent extraction



Sept. 17, 1940. M. J. LIVINGSTON ET AL 5 OLVENT EXTRACTI ON Filed June 10, 1936 Anhydrous pheno/ rm r a a m m ac m n v m mmw ye MHP Y Patented Sept. 17, 1940 UNITED STATES sonvnn'r nxmc'non Myran J. Hvingston, Mariners Harbor, N. Y., Henry 0. Forrest, Teaneek, and Percy 0. Keith, Jr., Peapack, N. 3., assignors to Standard Oil Company, Chicago, 111., a corporation of Indiana Application June 10, 1936, Serial No. 84,536

2 Claims.

This invention relates to solvent extraction and it pertains more particularly to the refining of mineral oils to produce high quality lubricants.

The object of our invention is to provide a simple counter-current extraction-system which will obtain maximum yields of high quality lubrieating oils from any given stock, and which, by the same sign, will reject a relatively small amount but nevertheless all of low gravity extract material. In other words, our primary object is to improve the efiiciency of counter-current extraction systems and to prevent the loss of desirable paramnic oils with extract material.

A further object is to increase the efllciency of counter-current extraction towers by providing specific types of packing therefor. Where 011 is the continuous phase in the tower our object is to provide a packing material which will be prefe'r entially wet by the oil and where solvent is the continuous phase we prefer to employ a packing which will be preferentially wet by the solvent. A further object is to determine the optimum size of Lessing rings, Raschig rings, saddles, etc., em-

ployed for packing, and to provide the proper arrangement of said packing in the tower.

A further object is to provide a solvent modification at the extract end of the tower which will act in a manner similar to the action of a reflux liquid in the top of a distillation tower. In other words, our object is to release all of the good oil from the extract in the extract end of the tower without introducing any contaminant or additional solvent into the ramnate end of the tower. We want to avoid the use of so-called paraflinic solvents in counter-flow to the naphthenic solvent because the paramnic solvent in such systems is undesirable in the raffinite end of the tower; we seek to change equilibrium conditions in the base of the tower without unduly altering equilibrium conditions in the top or the tower and without contaminating the raflinite with a parailinic solvent.

We may accomplish our objects in a packed counter-current phenol extraction tower by introducing a small amount of water in the extract end of said tower. This added water combines immediately with the solvent and radically modi fies its solvent characteristics, causing it to release all parafilnic 01] components and also to release some naphthenic components. These released paraflinic and naphthenic components which were being carried to the bottom of the tower with the extract thus reverse their course and flow upward toward the top of the tower. In this upward flow the naphthenic components are redissolved in the downcoming solvent-extract and there is a constant interchange of parafllnic and naphthenic components between the two liquid phases just as there is an interchange of higher boiling and lower boiling components in a rectifying tower which is being supplied with reflux liquid. The

addition ofwater at the base oi the tower acts as a control valve to eiIectlvely prevent the loss of parafllnic oils. The aqueous solvent does not get to the top of the tower, however, and in the railinate end 01' the tower the solvent still consistsof substantially anhydrous phenol. There is an increase in the naphthenic character of the oilin the lower section of the tower below the point of admission of fresh charge due to the injection of the water and this naphthenicity gradually changes in the tower from the top to the point of waterintroduction. It will thus be seenthat we have accomplished in a single tower what has hitherto required the use of a plurality 'of contacting and separating chambers and we have made possible the use of this gradually increasing naphthenic content of the oil from the top to the bottom of the tower to provide a more perfect fractionation than has ever before been possible. 3

Our invention also contemplates the use of a metal packing material such as nickel, nickel iron alloys, stainless steel, nickel plated material, etc., in those parts of the system where oil is the continuous phase, and wherein the solvent-extract falls in droplets therethrough. It is not essential to have packing material in the lower end of the tower; if such packing material is employed where the solvent constitutes the continuous phase and released oil must move in droplets upwardly therethrough, we prefer to use a packing material such as glass, porcelain or stone tile, which is preferentially wet by the solvent-extract material. In the lower end of the tower and/or in the portion of the tower wherein liquid separation is to occur, we prefer to employ larger packing elements than are used in the upper or more remote portions of the tower. The inventtion will be more clearly understood from the following description of preferred embodiments and from the enclosed drawing which diagrammatically represents an elevation partially in section showing the arrangement of our preferred tower. I

Our invention is particularly applicable to the refining of lubricating oil stocks and it may be applied to stocks from any origin whatsoever, particularly the stocks from Mid-Continent, Coastal relatively free from asphaltor have been freed from asphaltic or resinous materials by deasphalting processes such as those in which the asphalt is precipitated from. the oil by treating with liquid propane, ethane, etc. Heavy residual stocks require a longer settling time and the charging rate with any given apparatus must be accordingly diminished. As a selective solvent we prefer to employ phenol or phenolic compounds. By employing substantially anhydrous phenol at the top of the tower and introducing water at the base of the tower we are enabled to obtain maximum yields of high viscosity index lubricants. It should be understood, however, that instead of water we may employ methyl alcohol, ethylene glycol, or equivalent solvent modifier which is readily miscible with the solvent and which is effective in markedly decreasing its solvent power for parafilnic oil components. Our invention is likewise applicable to the use of cresols, cresylic acid, furfural, pyridine and other well-known selective solvents for removing naphthenic from parafiinichydrocarbon constituents, the liquid introwith the solvent and effective in reducing its solventproperties as hereinabove described.

Our present invention is not concerned with pumping, mixing and distributing means which may be employed in the system prior to the countercurrent tower or to solvent recovery means, clay contacting systems, etc., which may be used subsequent to the counter-current treatment. The description of our invention will therefore be limited to the counter-current tower itself, to the materials added thereto and removed therefrom, and to the treatment which takes place therein. 1

A commercial tower in accordance with our invention' may be about 40 to 60 feet high and about .4 to 8 feet in diameter, depending largely upon the amount and nature of stock to be treated. Thus we may employ a vertical cylindrical tower I0 about six feet in diameter and fifty feet tall, the top /3 to of the tower being preferably packed with Lessing or Raschig rings I I supported on perforated trays l2. which form the double function of redistributing the upflowing liquids and supporting the packing material so that the lower rings will not be crushed by the mass of a large column of rings above them. The base of the tower maybe entirely open and used as a separating chamber. It is preferred, however, to be provided with aperforated tray is supporting packing material l5 below liquid interface l6, as shown in the drawing.

Feed stock is introduced through line I! or through branch i8 or branch. l9 and is distributed in a column by any conventional or suitable means 20. Anhydrous phenol is introduced at the top of the tower through line 2| or branch lines Her 23 and phenol distributors 24. Water or other solvent modifying liquid is introduced into the lower part of the tower through line 25 or branch lines 26 or 21 andwater distributors 28. Rafllnate is removed from the top of the tower through line 29. Extract is removed from the bottom of the tower through line 30.

The solvent to oil ratio will usually vary from about 1:1 to about 2:1, and the amount of water introduced at the base of the tower is preferably about 4 or 5%, based on extract solution. The charging rate to the tower should be sufficiently rapid to obtain good counter-current contacts and sufficiently slow to efiect the necessary separation of solvent-extract phase from the oil phase. The temperature prevailing within the tower may differ with diflerent stocks and with different objectives and in general is between about and 200 F.; for neutral oils and similar light distillate stocks we prefer to operate at a top temperature of about 140 to 150 F. and a bottom temperature of aboutto F.

The solvent may be distributed by introducing apart of it thru branches 22 and 23, thus obtaining stage" treating in the tower, insuring intimate contact and minimizing the amount of solvent required.

1 The lower packing in the upper part of the tower preferably consists of 1" to Leasing rings or similar materials made out of metal, preferably nickel, nickel plated material or nickel alloy. We have found that nickel is quite remarkable in its tendency to be wet by the oil and not'by phenol. An excellent contact can thus be obtained by employing a packing material of nickel. We may employ stainless steel or other metal material and instead ofusing rings we may employ Jack chains, spiral springs or any other known form of packing. I a

In the upper part of the tower we prefer v employ half inch rings or other packing material of relatively smaller dimensions. Here also the material should be preferentially wet by the oil. Y

As above stated, the bottom of the tower may be left entirely open to serve as a settling space, but if packing material is employed to increase the effectiveness and the distribution of the added water, we prefer to employ glass beads, jackstones, porcelain rings, etc., of relatively large dimension.

A very important feature of our invention is I the addition of waterto the tower itself so that there is a naphthenic content gradient from the bottom to the central or upper. part of the tower. The water injected into the system through distributors 28 causes immediate 1 release of relatively large quantities of oil which thereupon flow upwardly in the form of small droplets through packing material 15 which is wet by the solvent extract liquid. This upflowing material tends to accumulate paraf'flnic oil from the solvent and carry it upwardly inthe tower, thus effecting the separation of parafilnic oil from solvent even before th olvent reaches the bottom of the tower. s upside-down reflux has proved to be very eifectlve in improving yields of high quality oils obtainable in a single counter current tower in any given stock.

As an example of our process, we may employ a Coastal distillate feed stock having a gravity of 19.4, a Saybolt viscosity at 210 F. of '12 and a viscosity index of 15. Using a phenol to oil ratio of about 1.25:1, a top temperature of about F. and bottom temperature of about 120 F. we obtained the following interesting comparison:

When no water is introduced at the base of the tower we obtain a rafllnate yield of 61.6%, this oil having a Saybolt viscosity at 210 F. of 67, and a viscosity index of 58. When 4% water isintroduced at the base of the tower the rafflnate yield is increased to 69.6% and the oil has a viscosity at 210 F. of 67.7 and a viscosity index of 55. When no water is employed the extract has an, A. P. I. gravity of 12 and when 4% water is used the smaller volume of extract has an A. P. I. gravity of 10.6. I

As another example of our process, we may asiasso extract a Mid-Continent distillate having an A. P. I. gravity of 26.2, a viscosity at 210' I. of 56.7 and a viscosity index of 78. Using a phenol to oil ratio of 1.29:1, a top temperature of about 150 F. and a bottom temperature of about 1125' R, we 11nd that without water we obtain the extract with 4% water added at the base of the tower is 9.1 A. P. I.

When residual stocks are extracted we prefer to use higher tower temperatures. Preferably about 175 1". to 200' F. at the top and to F. at the base. If the heavier oils are treated in the presence of a diluent, however, the higher temperatures are unnecessary.

The oils which have been solvent extracted, as hereinabove described, may be percolated through contacting clay (Riverside," "Att'apulgus," etc.) to obtain any desired color. Also, it may be dewaxed and/or subjected to other conventional refinery treatments.

.When we are refining Pennsylvania neutrals by our process the increase in yield is from about 93.2% to 95.4%. The significance of this increase becomes more apparent, however, whenwe consider that the amount of extract material is decreased from 6.8% to 4.6%; we are able to recover about a third of the material which would otherwise be lost, and our final extract has an A. P. I. gravity of only about 12 instead of 1 While we have described in detail a further embodiment of our invention. it should be understood that we do not limit ourselves to any of the details hereinabove set forth. It should also be understood that with diiierent selective solvents we may employ diiierent modifying liquids. For example, if furiural is employed as a selective solvent we may use acetone instead of water as a modifier in the base oi the tower.

We claim:

1. The method of solvent extracting a mineral oil in a vertical packed tower which comprises introducing substantially anhydrous phenol near the top of said tower, removing raflinate from the' top of. said tower. removing extract from the bottom of said tower, introducing water into the tower near the bottom thereof, introducing oil into thev tower at an intermediate point thereof, regulating the flow of liquids in the towertomaintain a liquid interface near the bottom of said tower and to prevent the introduced water from reaching the top of said tower, contactingthe counter-flowing liquids abovethe position of said interface with a packing material preferentially wet by oil, and contacting the counter-flowing liquids below the position of said interface with a packing material preferentially wet by aqueous phenol.

2. The method of claim 1 wherein the packing material which is preferentially wet by oil comprises nickel and wherein the packing material below the liquid interface is a vitreous packing material.

man J. LIVINGSTON. HENRY O. FORREST. PERCY 0. mm. la. 

